Sunglasses have widely been worn by people to prevent sun from directly shining into their eyes. Another reason for people to wear sunglasses is to have a so-called "cool" feeling. Sunglasses of the prior art, as shown in FIG. 5, generally include two lenses B permanently clamped into two recesses A1 of a frame A. The frame A has two female channels at respective opposite ends adapted to interlock with two male channels of two bows C. The lenses B are generally made from glass, which is fragile and easily damaged. When a lens becomes damaged, it is necessary to discard the entire glasses, which is impractical.